If $$A = \begin{bmatrix} 1 & -1 \\ 2 &  -1 \end{bmatrix}, B = \begin{bmatrix} a &  1 \\ b & -1 \end{bmatrix}$$ and $$(A+B)^{2} = A^{2} + B^{2}$$ , then a + b =

A

5

B

-4

C

4

D

-5